/Engine/Source/Runtime/NavigationSystem/Public/NavigationData.h
Calculates path from PathStart to PathEnd and retrieves its length.  this function does not generate string pulled path so the result is an (over-estimated) approximation  potentially expensive, so use it with caution
virtual [ENavigationQueryResult::Type](API\Runtime\Engine\AI\Navigation\ENavigationQueryResult__Type) CalcPathLengthAndCost ( const FVector & PathStart, const FVector & PathEnd, [FVector::FReal](API\Runtime\Core\Math\TVector\FReal) & OutPathLength, [FVector::FReal](API\Runtime\Core\Math\TVector\FReal) & OutPathCost, FSharedConstNavQueryFilter QueryFilter, const [UObject](API\Runtime\CoreUObject\UObject\UObject) * Querier ) const